Just hours after a campus officer at the Massachusetts Institute of Technology was shot and killed, multiple agencies descended upon a neighborhood outside Boston after explosions were reported.
The Boston Police Department described the situation as "an active incident" and is urging residents in Watertown, Mass., to remain in their homes.
State police spokesman David Procopio said, "The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers."
Witness reports say the suspects were throwing explosive devices during a car chase with police.
A reverse 911 call was sent out urging residents to stay inside, lock their doors and refuse to answer anyone who is not an identified police officer.
Boston police sent a tweet at 4 a.m. Eastern Time to say that police plan to go door-by-door, street-by-street in and around Watertown.
Dozens of officers from many agencies, including members of the National Guard, are now in Watertown, which is about 10 miles west of Boston. FOX News reporters in the area reported hearing gunfire and explosions early Friday morning.
Witnesses told the Associated Press they heard multiple gunshots and explosions at about 1 a.m. A helicopter is circling overhead, and reporters in the area are being instructed to turn off their cell phones.
Early Friday morning, authorities were ordering someone to get on the round and put their hands up when a loud thud was heard after someone shouted "fire in the hole."
Reporters are being told to move away from the scene. A police officer told a reporter: "If you want to live, turn off your cell phone."
Federal agents are on the scene, and they are investigating a link between the shooting at MIT, a carjacking nearby, the manhunt in Watertown and the Boston Marathon bombing. At this point, they said a suspect in custody shares "features" with the images of the suspects released.
The Associated Press is reporting that one of the two suspects sought in the MIT officer shooting is dead, and that the second suspect sought is linked to the Boston Marathon bombing. Several media outlets are reporting that the FBI's suspect No. 2, seen wearing a white hat in photographs released Thursday, is currently being sought.
Information from the Associated Press was used in this report.